In the construction of buildings with so-called dry walls, it is conventional to apply a joint compound to the joints of wallboard panels to conceal the joints and present a monolithic surface. It has also been conventional to use either a setting type of compound or a drying type of compound, or both, depending upon construction conditions, such as the rate at which the joint must be ready for further treatment or handling, atmospheric moisture conditions, and others. Settings types of compounds are characterized by a material, such as calcium sulfate hemihydrate, which reacts with some of the water in the compound to convert the hemihydrate into the dihydrate. Drying is incidental and in some cases undesirable. An example of a setting type of compound is disclosed in U.S. Pat. No. 3,297,601. On the other hand, drying type compounds do not react with the water, but rely on the evaporation of the water to give them strength. That is, instead of having a hemihydrate filler, calcium carbonate is often used. Such drying types usually incorporate a binder such as polyvinyl acetate, which when dry contributes the primary strength against stress needed by the compound. An example of a drying type is disclosed in U.S. Pat. No. 3,342,761.
Particularly in drying type joint compounds, it has been required heretofore that mica be incorporated to prevent cracking due to shrinkage. For example, United States Gypsum Company sells a Ready-Mix All-Purpose Joint Compound at its New Brighton, New York City plant which uses as a filler terrra alba, that is, landplaster which has been sized to remove plus 100 mesh particles. Mica is incorporated in the formulation of that compound. Even with a slowly setting type of compound produced by Keene's cement, mica has been recited to be an essential ingredient, as otherwise the dried product exhibits unacceptable cracking. See, e.g., U.S. Pat. No. 2,662,024. As a component which must be added, mica represents an additional cost which would be advantageously omitted, if possible. Further, it tends to increase the consistency of the final mix, thus requiring an increase in the amount of water that is required.